This invention relates to root canal therapy and in particular to the removal of a broken tool or instrument fragment lodged in the pulp chamber or root canal of a tooth.
The pulp chamber contains the pulp tissue which comprises the circulatory, connective and nerve tissue of a tooth. The pulp tissue extends from the jaw bone through one or more root canals inside each tooth to a pulp chamber. It may become necessary for a dentist or endodontic specialist to remove diseased or injured pulp tissue from root canals so that a patient can retain an original tooth in situ. Therefore a primary objective of root canal therapy is to obviate a tooth extraction procedure and its accompanying trauma to surrounding tissue and bone. As part of the therapy, the endodontic clinician removes the pulp material and shapes the root canal prior to inserting filler material in place of the original pulp.
The dental clinician must have fine dexterity and extensive training to perform a pulp extirpation successfully as root canals are very small and the canals themselves are often curved or irregularly configured. In conventional practice the clinician removes at least a portion of the crown of a tooth using a rotary bur or similar instrument to expose openings to the root canal. Small, tapered metal tools or instruments, generally referred to as files, are inserted into a root canal to remove the pulp. Files are available having different metallurgical composition and different mechanical characteristics. A manually operated file is comprised of a handle and a shank, the working end of the tool. The shank is commonly manufactured from very thin wire made from an alloy of nickel-titanium or stainless steel. The wire is helically wound and extends out from the central axis of the handle approximately 5 mm. Files are usually supplied in numbered and colored sets where the number or color on each file handle corresponds to a characteristic of a particular file. Each file in a set may differ slightly in maximum working diameter and each may serve a different specific purpose in the debriding procedure.
In practice a clinician commonly uses the fingers of one hand (usually the thumb and forefinger) to manually insert a file into the exposed opening of a root canal. The file is rotated to engage the pulp tissue while it is simultaneously being moved up and down, carrying out tissue debris and progressively enlarging and shaping the canal space. Other files are designed as reamers to enlarge a canal to a fixed diameter. A typical shank end of a file is 1 mm in diameter at the juncture with the handle and it may taper to a mere 0.2 millimeter in diameter at the tip, or distal end. Such miniscule files are quite prone to break and can become wedged or embedded in the interior dentinal wall of the canal which delays completion of normal therapy. This kind of breakage event requires additional remedial procedures and may ultimately lead to iatrogenic medical complications.
The prior art reveals a number of methods and devices available to the endodontic clinician to recover or remove a broken file. Special mechanical devices for this purpose may be manipulated directly by hand or a device may be attached to a vibratory (ultrasonic) handpiece of a kind available in most dental operatories. There are many commercial vendors and manufacturers of vibratory and ultrasonic dental handpiece devices including, as examples, Sybron Dental Specialties of Orange, Calif., Giulin Woodpecker Medical Instrument Co, Ltd of Guangxi, China, and Satelec Dental Equipment of the Acteon Group in Bordeaux, France.
U.S. Pat. No. 7,080,981 B2, issued to Terauchi in 2006, describes one such device together with accompanying implements for removing a broken instrument from a root canal. One of the Terauchi devices comprises a handle with a fork-shaped cutting end which is used to cut the internal dentin down to expose the head of the embedded broken instrument. Subsequently, after the head is exposed, a second instrument incorporating a stainless steel wire loop is used to effectively “lasso” the broken part enabling it to be withdrawn from the canal space. Other supporting instruments are also described which use tool tips designed for use with an ultrasonic handpiece to abrade or cut the area surrounding the embedded broken tip enabling the use of the wire loop device. While there may be situations in which a clinician could actually catch a broken part in this fashion, it is always desirable to limit destruction of the surrounding dentin as much as possible to better preserve the tooth. If an embedded part is actually free enough to be grabbed, a more conventional and common approach utilizes a very small forceps known as a Steiglitz forceps to grasp a broken piece without having to resort to lassoing.
A patent application publication, U.S. 2003/0157458 A1, by Buchanan describes a number of dental instrument tool tips for performing endodontic procedures. Some of the tips illustrated have abrasive coatings and others have radiused ends to minimize troughs and scratches within the root canal when the tips are used in conjunction with an ultrasonic handpiece. Buchanan discloses tool tips for ultrasonic dental handpieces which are described as less prone to damage a tooth. Inadvertent damage to tooth structures using various kinds of vibratory handpieces is a common and continuing problem in the field of endodontics. Root canals are dimensionally minute, and even well-trained and manually adept clinicians do not have perfect physical control using vibratory instruments within the canal space. As a consequence, abrupt or unintentional movements may cause unwanted removal of dentin material. When scratches and troughs or “ledges” are carved within the canal, small voids are created which are difficult to see even with the aid of dental magnifiers. Therefore it becomes difficult to fully extirpate and sanitize the canal for purposes of complete obturation. If left unfilled, these voids can become repositories for harmful bacteria. In the Buchanan invention, the tool tips are fixedly attached to the ultrasonic handpiece either by a threaded connection or by a mechanical interlock typically used to chuck a driven tool. As such, small erroneous movements by the clinician using an ultrasonic handpiece—even one equipped with Buchanan's less damaging tool shapes—may well induce unwanted material removal and damage to canal surfaces,
Another approach to endodontic treatment depicted by Laufer in U.S. Pat. Publ. 2014/0080090 employs what might be called a waterjet in miniature. Laufer shows a dental handpiece which drives a rotary device that creates a vortex-like “micro-tornado” where water mixed with an abrasive is forced through a small cannula to remove pulp and debris and diseased tissue. This device would be new to endodontic therapy and it remains to be seen whether micro-tornadic jets of water-borne slurry can be manipulated accurately enough to perform effectively in standard endodontic clinical practice. If pressures sufficient to remove calcified dentin are achievable through a micro-cannula of this nature, then the same limitations of an ultrasonic handpiece with a rigidly fixed end tool would apply to the micro-tornado device. Slight inadvertent movements by the clinician may have quite adverse consequences for a patient's tooth.
A different unconventional approach, U.S. Pat. No. 7,677,892 B2 (2010) awarded to Alexandrovskiy et al. describes how two electrodes shaped into a small cylinder can be inserted into a root canal to weld the broken piece of a file to the tip of one of the electrodes. The broken file is thereby unified with the electrode and this combination can be withdrawn from the root canal interior. While the concept of welding broken pieces together sounds plausible, in actual practice manipulating an electrode in a curved root canal so that it contacts some deeply embedded file fragment may in many instances be clinically unachievable. At the present time this technique is not commonly used in domestic endodontic practice.
A technique analogous to, and referenced by Alexandrovskiy et al. is used to dissolve a broken file tip electrochemically by the continuous application of electric current. However this electrochemical technique has a tendency to exceed physiologically acceptable temperatures within the confines of a root canal. It is also difficult for the patient in the operatory because it requires a relatively long time to work effectively and can contribute to undesirable toxic aftereffects.